Yes, IRIS is a Scrabble word!

Letter values in Scrabble US: I 1, R 1, I 1, S 1.

Is it a valid word?

IRIS is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

plants with sword-shaped leaves and erect stalks bearing bright-colored flowers composed of three petals and three drooping sepals
muscular diaphragm that controls the size of the pupil which in turn controls the amount of light that enters the eye; it forms the colored portion of the eye
diaphragm consisting of thin overlapping plates that can be adjusted to change the diameter of a central opening

Also: fleur-de-lis, sword lily, iris diaphragm.